351w milky oil and h2o in cylinders cant find the issue

guys a buddy of mine threw some new exhaust manifolds on his boat last season. the manifolds had only one bolt per port(there are 2 holes on the head side and all my boats have had 2 bolts per port) holding it to the head which i thought was weird but the original manifolds are the same way. so anyway he winterized the boat in october and took it out this summer and and noticed water in the oil. he yanked of the intake manifold and put it back on, improperly i believe.
so anyway i pulled the heads off last night expecting to find a blown gasket and it was not blown but i did find water in 4 cylinder heads(the 2 rear cylinder heads on the port and starbd sides). i dont suspect a cracked block, everything looks just fine. im at a loss. possibly a hole in the intake manifold? could the exhaust manifolds be the issue?

Exhaust could have heated up and caused a reverse suction when the boat was turned off and pulled water back into the engine... Seen it a couple times this year already....

the single whole per port is standard on some engines, mine is the same way. how did the intake look when you pulled it off? Water flows thru the intake as well, and if he put it on incorrectly, could be the issue...

ya I had the same problem. pulled all the plugs let the water drain, then turned the engine with the plugs out till no water came out. Cleaned plugs, changed oil and great! Mine was due to a cracked water pump which cause the engine to overheat and thus turning the exhaust into an intake sucking in water and forcing into the cylinder heads. Pretty common and an easy fix. But if it is doing it all the time...you got something else wrong.

Dealing with the same problem right now. Blew an impeller, overheated the boat and hydrolocked it. We pulled the plugs, there was water in three of them and turned it over.

The shop called me yesterday and said that the compression was all normal so they don't think it blew a head gasket, but there was water in the oil.

I'm still waiting to hear back from them. Once I do I'll post back with an update.

I have a 351, GT-40...

same thing happened to me a couple years ago. Impellor siezed, engine got hot and Hydrolocked ( sucked water into the cylinders) Drained all oil and changed plugs and has been fine since. Oh yea I also put in a new impellor (obviuosly) Hopefully this is all thats wrong.

intake manifold looked good. i didnt do a very good inspection though. impeller is fine. ill check the water pump next for cracks.

So I got mine back yesterday. The shop basically just changed the oil three times. I took it out and ran it for about 2 hours and it ran fine. Only area of concern was that the temp was a little hotter than normal, typically around 160 and it was mostly running around 175. I'm thinking I'm going to sway out the thermostat and see what happens.

Crazy, I originally thought I had either seized my motor or blew a head gasket. Got really lucky. Needless to say, I'll be switching the impeller every season now.